Apparatus for applying heat-fusible coatings on solid objects



Nov. 19, 1963 A. P. SHEPARD ET AL 3,111,267

APPARATUS FOR APPLYING HEAT-FUSIBLE COATINGS ON SOLID OBJECTS FiledApril 18, 1957 4 Sheets-Sheet l INVENTOR ARTHUR I? SHEPARD FERDINAND J.D/TTR/Ch' BY g Dulu v p ATTORNEYS APPARATUS FOR APPLYING HEAT-FUSIBLECOATINGS ON SOLID OBJECTS Filed April 18, 1957 Nov. 19, 1963 A P.SHEPARD ETAL 4 Sheets-Sheet 2 INVENTORS ARTT/UR F. SHEPARD FERDINAND J.D/TTR/C BY flap, D@(1. o$ }m ATTORNEY 1963 A. P. SHEPARD ET AL 3,111,267

APPARATUS FOR APPLYING HEAT-FUSIBLE COATINGS 0N SOLID OBJECTS FiledApril 18, 1957 4 Sheets-Sheet 4 I EFWWM/ PRIOR ART /403 T ar=:.l4.-

INVENTOR ARHVUR P SHEPARD FERDINAND J DlTTR/CH ATTORNEYS United StatesPatent 3,111,267 APPARATUS FOR APPLYING HEAT-FUSIBLE COATING-S 0N SDLIDOBJECTS Arthur P. Shepard, Flushing, and Ferdinand J. Dittrich,Bellmore, N.Y., assignors to Metco Inc, a corporation of New JerseyFiled Apr. 18, 1957, Ser. No. 653,662 3 Claims. (Cl. 239-85) Thisinvention relates to an apparatus for applying heat-fusible coatings onsolid objects from heat-fusible materials in divided, such as powdered,form. The invention more particularly relates to a gun construction forspraying heat-fusible material, using a fuel gas and a combustionsupporting gas where said material is fed into the gun in finelydivided, solid form.

Heat-fusible material spray guns of the powder type are devices in whichpowdered material is fed to a heating zone wherein it reaches a moltenor at least heatplastic condition, and from which it is propelled, at arelatively high velocity, onto the object to be coated. Heat-fusiblematerial spray guns of this type provide means for conveying thepowdered material to be sprayed from a hopper to the heating zone by astream of gas, in which the finely divided powdered material isentrained.

Such guns are most commonly used for spraying metal powders and henceare frequently referred to as powdertype metal spray guns.

All of the previously known powder spray guns and the methods ofspraying the powder used thereby have been subject to certainfundamental limitations. Some guns of this type have been satisfactoryonly for spraying very low melting point materials. New guns have beendeveloped, however, which are satisfactory for spraying higher meltingpoint materials, such as nickel base alloy metals and refractory ceramicmaterials, including alumina and zirconia.

These guns, which are satisfactory for higher melting point materials,differ from previous powder spray guns it. that they supply the powderedmaterial to the center of the flame at a relatively low velocity and doso by using a relatively small amount of carrier gas in proportion tothe solid material carried.

All previously known heat-fusible material spray guns and sprayingmethods have been subject to certain fundamental limitations, however.All such previously known guns, for instance, are very critical tooperate with high melting point materials. The carrier gas pressure andvolume must be adjusted very accurately, and the flow of solid powderedmaterial to be sprayed must be adjusted and controlled very accuratelyto produce satisfactory coatings. This requires a well trained, highlyskilled operator, since it is extremely difiicult to tell when theseadjustments are properly made. For instance, when spraying refractoryceramics, if the velocity of the carrier gas as it enters the flame isslightly too high, then soft coatings result, and if it is slightly toolow, coatings with large spattered lumps of material result. Since thisadjustment is very critical, the operators must frequently producespoiled and defective coatings in order to get the gun adjustedproperly. Some operators have been unable to consistently producesatisfactory coatings.

Another limitation of even the most etlicient previously known guns isthat they require very accurate grading in 3,1 l 1,26 7 Patented Nov.19, 1963 a narrow range of the particle size of the material to besprayed. For instance, with such guns alumina must be graded to aparticle size range of from 10 to microns, and zirconia must be gradedfrom 10 to 40 microns. Even when accurately so graded, materials of thistype give the ditliculties described above when sprayed. Grading thesematerials accurately is very expensivenot only because of the cost andtime required for the grading operation, but also because only a verysmall amount of the original commercial material can be used forspraying and the balance must be discarded.

The construction and method in accordance with this invention overcomesthe aforesaid limitations and difficulties.

The construction and method in accordance with this invention makes itpossible for the first time to spray refractory powdered materials(including refractory metsis and refractory ceramics) so that consistenthard coatings can be produced without spatter by unskilled operators.

The construction and method in accordance with this invention makes itpossible for the first time to spray refractory powdered materialscomprising a relatively wide range of particle sizes and particularlyfiner materials than previously have been sprayable. For instance, whensprayed in accordance with this invention, alumina of a particle size offrom 2 to 60 microns, and zirconia of a particle size of from 2 tomicrons, may be successfully sprayed commercially.

In accordance with this invention carrier gas containing finely dividedsolid heat-fusible material is introduced into the central zone of aheating flame, such that the velocity of every part of the cross-sectionof the stream of said gas is essentially the same and whereby said gasand the entrained particles of said material are diffused throughout thecross-section of said flame.

The spray gun nozzle for effecting the method in accordance with thisinvention has means for passing a combustible fluid and a combustionsupporting fluid, such as gases, with a substantial forward linearvelocity for flame combustion from the tip of said nozzle, a carrier gasconduit terminating substantially adjacent said tip of said nozzle, saidconduit being positioned and adapted for introduction of carrier gasinto the central zone of said flame, and diffuser means in said conduitcooperatively positioned with respect to said conduit to diffuse saidcarrier gas throughout said flame and thereby distribute said materialevenly into said flame.

For purposes of illustration and not of limitation, the invention willbe described in further detail with reference to several preferredconstructional embodiments, as shown in the drawings in which:

P16. 1 is a side elevation of one embodiment of a heatfusible materialspray gun in accordance with this invention;

FIG. 2 is a vertical longitudinal section of the embodimerit of FIG. 1;

FIG. 3 is an enlarged partial cross-section of FIG. 2;

FIG. 4 is a front elevation of the showing in FIG. 1;

FIG. 5 is a plan view, partially in section, of the underside of FIG. 2;

FIG. 6 is a vertical cross-section of the nozzle of the embodiment shownin FIG. 2;

FIG. 7 is an end view taken in the direction 77 of the showing of FIG.6;

FIG. 8 is a cross-section of the nozzle of a heat-fusible material spraygun showing an alternative embodiment of the invention;

FIG. 9 is an end view taken in the direction 9--9 of the showing of FIG.8'.

FIG. 10 is a cross-section of the nozzle of a heat-fusible materialspray gun showing a preferred embodiment of the invention;

FIG. ii is an end view taken in the direction lit-11 of the showing ofFIG. ltl;

FIG. 12 is a cross-section of the nozzle of a heat-fusible material gunshowing an alternative embodiment of the invention;

FIG. i3 is an end view taken in the direction l3.l3 of the showing ofFIG. 12;

FIG. 14 is a schematic diagram illustrating the flame of a previouslyknown heat-fusible material spray gun; and

FIG. 15 is a schematic diagram illustrating the flame of a spray gun inaccordance with this invention.

Referring to the drawings, 1 shows the body of the spray gun, on whichis mounted the inclined, tubular material hopper 2. Material hopper 2 isheld by a saddle 3 (FIG. I) fastened to body 1 by a through-pin 4, whichis threaded into saddle 3 at one end to hold it securely in place. Theentire hopper 2 with its saddle 3 can be removed for convenience byremoving threaded pin 4. A hole 5 (FIG. 2) is provided in the hopper 2in communication with the duct 6 in saddle 3. A valve block 7 issecurely mounted on top of body 1 and provided with duct 8, which is inline with duct 6. A nipple 9 is mounted between block 7 and saddle 3, soas to connect ducts 6 and 8. The nipple 9 is held in place by a plate 10and screws 11. A packing washer 12 is provided around nipple 9.

A small piece of rubber tube 13 fits over the lower projecting end ofnipple 9 and is held in place by a rubber ring 14. A valve chamber 15 isprovided in block 7 and is fitted with a piston 16, having the packingrings 17 and 18.

The piston 16 is operated by a valve-operating mechanism which will bemore fully described hereafter.

The body 1 is provided with a powder feed chamber 19, a longitudinalbore 20 extending centrally through the front end of the body, back toand communicating with a central duct 21 and a hole 22 communicating thepowder chamber with the bore 20.

A seat plug 23 in the form of a cylindrical, flanged plug is fitted intothe bore 20 with a sliding fit and has a flange extending over the endof body 1. The body 1 is provided with a threaded section 24, onto whichis threaded a nut 25. A nozzle 26 is mounted on the flange of seat plug23 and held in place by nut 25, which simultaneously holds seat plug 23in place.

The nozzle 26 has a central bore 27 which communicates with the centralconical bore 28 of seat plug 23 in such a manner that the two form acontinuous extended bore. A groove 29 is provided in seat plug 23 on theupper half only and communicates bore 28 with hole 22. A jet screw 39 iscentrally located in seat plug 23 and is screwed into a central threadedhole in seat plug 23. The jet screw 30 is provided with a small centraljet hole 31 which is concentric with the bore 28 of seat plug 23.Packing rings 32 and 33 are provided to seal seat plug 23 in the bore 20at both sides of groove 29.

A dowell pin 34 is provided between body 1 and seat plug 23 to hold itin a predetermined position.

A bleeder hole 35 is provided from powder chamber 19 to the front end ofbody 1. The nozzle 26 (FIG. 6) is provided with an annular groove at itsbase 36 and a multiple number of parallel nozzle jet holes 37, arrangedin a circle. Nozzle 26 is also provided with air holes 38, which arelocated alternately between holes 37 and terminate inwardly of holes 37,nearer to bore 27, and extend at a relatively steep angle to the outersurface of nozzle 26.

The seat plug 23 is provided with a hole 39 through its flange, whichcommunicates with annular groove 36. Body 1 is provided with duct 49which communicates with hole Body 1 is provided with duct 41 forcombustion supporting gas and duct 42 for combustible gas. These duetscan be seen by referring to FIG. 5 which also shows more clearly theconnecting ducts between ducts 41 and 4 with duct 45).

The connecting duct between 4! and 41 is the connecting duct 43, and theconnecting duct between 40 and 42 is the connecting duct 44. These ductsare provided by cross-drilling through body 1 and plugging the outerends oi" these ducts with small steel screws at 45 and 46. Valves 47 and43 are provided and mounted on the rear of. body 1 by means of mountingplate 49 and screws 50. These valves are arranged to communicate withducts 41 and 42 respectively, and these connections are sealed bypackings 5i and 52 respectively.

A valve 53 is provided and mounted on body 1 by means of screws 5-4. Thedetails of this valve construction can best be seen in FIG. 3. Acylindrical bore 55 is provided in body 1 for mounting of this valve.The valve consists of a valve body 56, into which is threaded a needlevalve needle 57. on which is secured valve handle 58. Packing ring 59seals between the inner bore of valve handle 58 and the body 56. Body 56is provided with a conical seat 64 into which the needle of the needlevalve 57 fits. Body 56 is provided with packing rings 61 and 62, whichare spaced on each side of a groove 63 on the outer cylindrical surfaceof body 56. A hole 64 is provided from the bottom of the bore 55 intoduct d2 or a similar hole may be provided into duct 41.

Referring to FIG. 2, a small duct 65 is provided in body 1 connectingbore 55 with central duct 21 and terminating in bore 55 in directcommunication with annular groove 63 in valve body 56. Hole 90 connectsannular groove 63 with the bore in valve body 56.

A handle 66 is mounted on body 1 by means of screws 67. Screws 67 alsohold mounting bracket 68, which extends to one side of the gun and hasstud 69 secured at its terminus. Mounting bracket 68 and stud 69 provideconvenient means for mounting the gun when it is not being used by hand.

A trigger 70 is connected through a mechanism, hereinafter to bedescribed, to valve piston 16. Pin 71 in body 1 pivotally supports thetrigger 70. Spring 72 holds trigger 70 in a forward position away fromhandle 66. Trigger 70 (FIG. 1) extends upward on both sides of the body1 and at its upper end is mounted a cross pin 73. Cross pin 73 engages aslot in hollow square piston 74. A housing 75 is mounted on body 1 byscrew 76 and defines a square piston chamber between itself and the toparea of body 1. A cam 92 is mounted on pivot pin 77 in housing 75 and isheld in a neutral position, as shown in drawing, by spring 78.

A secondary piston 79 slides in a bore provided in piston cylinder 74,and is held in a forward position by spring 80, which presses againstsnap ring washer 81, which is fastened to piston 79. A screw 82, whichis screwed into the bottom of piston cylinder 74, acts as a limit stopin both directions for secondary piston 79. Valve piston 16 has spring83 engaging housing 75 at one end and snap ring washer 84 at the otherend, so as to hold valve piston 16 in a rearward position.

The top of square piston 74 has a forward cutout see tion 85 and a rearcutout section 86 on its upper portion. These cutout sections, and theforward and rearward termini thereof, act to engage the cam projectionsof cam 92, as will be hereinafter more fully described.

Valve handle 58 is provided with milled grooves 87 which engage thepointed end of detent piston 88. Detent piston 88 slides in the spaceprovided for it at the rear of housing 75 and is pressed rearwardly byspring 89.

Trigger 70 operates to open and close a powder feed valve whichcomprises rubber tube 13 and the piston 16. In the closed position, withthe piston 16 in its rearward position, the piston squeezes the end ofrubber tube 13 closed. This position is shown in FIG. 2. When piston 16is moved to a forward position it releases the squeezing pressure on theend of rubber tube 13, opening it and permitting powder to flow throughthe rubber tube.

In the open position of rubber tube 13, powder is permitted to flow bygravity from hopper 2 through hole 5, duct 6, the passage in nipple 9,through rubber tube 13, through valve chamber and into powder chamber19.

When trigger 70 is pulled rearwardly toward the handle 66, pin 73 ismoved in a forward direction, causing cylinder piston 74 to move in aforward direction, carrying with it secondary piston 79, which alsotherefore moves forward. Piston 79 engages and also pushes forward valvepiston 16 and hence opens the valve. When valve piston 16 is all the wayforward, at the limit of its stroke, piston cylinder 74 continues tomove forward. This additional movement is permitted since aftersecondary piston 79 stops moving forward, spring 80 is compressed.During the forward movement of cylinder piston 74 the rearward terminusof cutout section 85 engages the lower projection of cam 92 and rotatesit clockwise until the rearward projection of cam 92 engages the rearterminus of cutout section 86 of piston cylinder 74. This stops theforward motion of the piston cylinder 74, and at this point the lowerprojection of the cam 92 is positioned just above the groove 85a in thepartition separating the cutouts 85 and 86. As the trigger 70 isreleased, the piston cylinder 74 is urged rearwardly by the spring 80.It, however, can only move a very short distance rearwardly before it isstopped by the engagement of the lower projection of the cam 92 in thegroove 85a, preventing further rearward movement. The valve thereforeremains in a locked, open position even after the trigger 70 isreleased.

To release the valve the operator simply again squeezes the trigger 70toward the handle 66 a second time. This causes forward motion of thepiston cylinder 74, which is permitted, since the cam 92 can rotateslightly in a clockwise direction and since the lower projection of thecam can slide out of the open, rearward end of the groove 85 into thecutout section 86. The lower projection of the cam 92 is already pastthe highest point on the partition separating the cutouts 85 and 86 sothat the rearward terminus of the cutout section 85 will not rotate thecam to a position where its rear projection will stop the for- Wardmotion of the piston cylinder 74 by contacting the rearward terminus ofthe cutout section 86. The operator then releases the trigger and thecylinder piston 74 and the trigger 70 will return all the way to theoriginal position as shown in FIG. 2. The rearward motion of the pistoncylinder 74 will merely cause the cam 92 to rotate in acounter-clockwise direction when the lower projection strikes thepartition separating the cutouts 85 and S 6, and after riding over thisprojection the spring 78 will cause the cam to snap back, with its lowerprojection in the cutout 85. The spring 80 will act to push the cylinderpiston 74 rearwardly only until the secondary piston 79 disengages thepiston valve 16. Thereafter the rearward motion is caused by the actionof the spring 72, which urges the trigger 70 forward and thus the pin 73rearwardly.

The trigger and powder valve mechanism thereby permits the operator toopen the valve by pulling a trigger a first time, and the valve willremain open even after the trigger is released. The valve is closed bypulling the trigger a second time and then releasing it.

In operation, the powdered material to be sprayed is placed in hopper 2,and fuel gas and combustion supporting gas hoses are connected in theconventional manner to valves 48 and 47 respectively. Sources of fuelgas and their hoses and fittings are not shown, since these areconventional and well known for use with such equipment. With the powdervalve just described closed, and the powder feed valve 53 closed, thegun is first lighted by slightly opening valves 48 and 47 and lightingthe gases as they emerge from nozzle jets 37.

The fuel gas flows through valve 48 into and through conduit 42, throughconnecting conduit 44 and into conduit 40. The combustion supporting gasflows through valve 47 and into and through conduit 41, throughconnecting conduit 43 and also into conduit 40, where it mixes with thefuel gas. The mixed gases flow from conduit 40 through hole 39 and intoannular groove 36, and from thence through multiple nozzle jets 37 Wherethey are ignited upon emergence.

The discharge of the gases from nozzle jets 37 causes reduced pressureat the face of nozzle 26, which causes objectionable turbulence at theface of the nozzle, which in turn tends to cause deposit of fusiblematerial on the face of the nozzle. When the nozzle is lighted, however,the reduced pressure at the face of the nozzle is substantially relievedby the induced flow of a small amount of atmospheric air through holes38, which terminate at the face of the nozzle in alternate positionsbetween nozzle jet holes 3-7. While the flow of air through holes 38 isvery small, it is suificient to completely eliminate the tendency formaterial to collect and build up on the face of nozzle 26.

To start the powder flow, valve 53 is first adjusted. The detent piston38 engaging the grooves 87 in valve handle 58, provides a convenientmeans for determining the setting of the valve by counting the number ofclicks from a fully closed position. The detent also securely holds thevalve in a predetermined position. When valve 53 is open, a small amountof fuel gas flows from conduit 42 through hole 64, through the valve 53,and past neec'ile as, into the bore of valve body 56, through hole 90,into annular chamber 63, and from thence through conduit 65 into centralduct 21. From central duct 21 a very small amount of gas is permitted toflow through jet hole 31 in jet screw 36. This jet of fuel gas extendsacross groove 29 and exhausts out through powder conduits 2S and 27 tothe center of the flame.

To start the powder feeding, the operator pulls back on tri ier 7%,which opens the powder feed valve as hereinahotc described. The powderthen flows from powder chamber 19 into groove 29, where it is picked upby the jet of fuel gas emerging from jet hole 31. The powder is thencarried forward through conduits 28 and 27 and emerges at the nozzleface in the center of the flame.

Hole 35 is provided into powder chamber 19 to maintain atmosphericpressure in said chamber. This is of importance since otherwise apartial vacuum is created by the action of jet 31, which varies with theflow of powder and hence causes an excessive variation in the powderfeed. Most metal powders feed satisfactorily by gravity from hopper 2down through the various passages to powder chamber 19 and groove 29.The hopper 2 has been mounted at an angle so that the material feedssatisfactorily for all positions of the gun through 90 from horizontalto practically vertically down.

The end or tip of nozzle 26- (FIGS. 6 and 7) has a counter-bored section60 1 which comprises a continuation of an enlargement of conduit 27. Atthe tip of the nozzle and at the terminus of conduit 601 is wire screen692. Screen 662 is fitted into the end of nozzle 26 by providing aslight additional counter sink to receive it. It may be fastened inplace in any conventional manner, such as by friction fit or brazing.Screen 60?. may be of a mesh size of from 20 to but is preferably of amesh size of from 30 to 50, and is most preferably a 40 mesh screen madefrom .06 diameter Wire.

An alternative embodiment of this invention may be seen by reference toFIGS. 8 and 9. In this embodiment nozzle 826 is similar to nozzle 26, inthat it has nozzle jets 837. In this embodiment, however, the internalconstruction of the nozzle differs from that shown in FIGS. 6 and 7. Inthis embodiment the nozzle 326 is counter-bored at 801. Into bore 801 ispress-fitted cylindrical diffuser plug 802. The forward cylindricalsection of plug 802 is somewhat smaller than counter-bore 001, so thatannular passage 803 is provided between plug 802 and bore 801. Annulargroove 804 is provided on the outer periphery of plug 802 and ispositioned to communicate With radial holes 805 in nozzle 826.

Nozzle 826 has conduit 827, which connects with an extension of thisconduit 806 in plug 802. The outer end of conduit 806 is taper-bored toa conical shape. A small cone 807 is centrally fixed in the conical boreof 005 so as to provide an annular conical groove or passage 800. Cone807 is supported by legs 809 which may be brazed to plug 802 and cone807 to hold it in position.

In operation the holes 805, groove 004, and annular passage 803 providea passage for atmospheric air which is drawn by the flame through thispassage. The function performed by this air is the same as that providedby air passages 38 shown in the embodiment of this invention describedin connection with P165. 2 and 6. However, in this construction the airis more evenly distributed, and it is possible to avoid the collectionof material on the tip, provide a more even flame, and use less air fordiluting and cooling the flame.

The construction in accordance with another embodiment of this inventionwill be seen by reference to H63. 10 and 11. In this embodiment of theinvention, the nozzle 1026 is externally similar to nozzle 26 and hasjet holes 1037 similar to jet holes 37 and conduit extension 1027similar to conduit extension 27. In this embodiment nozzle 1026 iscounter-bored to provide bore 100]. Into bore 1001 is press-fittedcylindrical plug 1002. Cylindrical plug 1002 is provided with a groove1004 and a smaller cylindrical section at its end to provide annularspace 1003. Communicating with annular groove 1004 are radial holes1005. The external plug construction and holes perform the same functionas the embodiment previously described in connection with FIGS. 8 and 9.

Plug 1002 is provided with bore 1006, which forms an extension ofconduit 1027. From conduit 1006 extending forward to the face of thenozzle are holes 1007. Holes 1007 are provided at an angle to the nozzleaxis so that they diverge toward their outer ends.

A still further alternative embodiment of this invention can be seenwith reference to FIGS. 12 and 13. The nozzle 1226 is similar inexternal construction to nozzle 26 and is provided with jets 1237similar to jets 37. Central conduit 1227 is similar to central conduit27 except that this conduit terminates before it reaches the flame tipof the nozzle. Extending from the terminus of conduit 1227 are holes1201. These holes 1201 have their axes on an angle so that they divergetoward the tip. So as to provide holes, the ends of which are at rightangles to their axes, the face of nozzle 1226 is turned slightly conicalat 1202.

Some powders, however, due to their configuration, size and otherproperties, do not feed as readily as other powdered materials. In caseswhere the powders tend to pack or feed unevenly, it is advisable toshake or vibrate the gun slightly. An extremely small amount ofvibration or shaking is required to cause smooth flowing of even thosepowders with the worst flowing characteristics. For this purpose, andwhen needed, a small vibrator, for instance an electric vibrator, suchas an electric buzzer, is attached to the bottom of the gun body, suchas by screws 91. Such vibrators are well known in the art and hence thisconstruction has not been shown in the drawings, nor is the vibratordescribed in detail.

While the hopper 2 may be made of any suitable structure and material,it is an advantage to make it of clear plastic material so that theoperator can see the amount of powder remaining in the hopper.

In place of the hopper 2, a separate, as for example, a larger capacityhopper may be supported above the gun and connected to the duct 6 bymeans of a flexible hose, as for example, a flexible rubber hose. Thepowdered heat-fusible material in the hopper, which is for examplesuspended from the ceiling, will feed through the flexible hose bygravity into the duct 6. This construction relieves the operator of thestrain of holding the weight of the heat-fusible material and allows theuse of a much larger capacity container. With such an arrangement thegun may be operated between a position pointing almost vertically downto a position pointing almost vertically up.

Powder ducts 27 and 28 cooperate to form a continuous section toward theoutlet and, together with the arrangement of jet hole 31 and groove 29,comprise carrier means which carry and introduce a large amount ofpowder into the center of the flame at a very velocity. This velocity isso low as to be negligible in comparison with the velocity of gases ofthe flame. The result is that the acceleration of the particles takesplace in the flame and through its hottest area. This results in thermalefficiency of a much higher order, as previously described. Materials ofmelting points as high as those of molybdenum, among the metals, andalumina and zir conia, among the ceramics, can be satisfactorilysprayed. Another result is substantially increased deposit efliciency.

When in operation, using the apparatus and method in accordance withthis invention, the carrier gas carrying entrained finely divided solidmaterial passes through its conduit and upon emergence from the nozzlediffuses outwardly into the flame at a rapid rate, so that finelydivided solid material is fairly evenly distributed throughout the flamecross-section. With previous metal spray guns, this result was notachieved. With previous constructions the finely divided solid materialwas delivered to the center of the flame by the carrier gas in a sharplydefined cone of carrier gas densely populated with material particles.Such a cone is illustrated schematically as 1401 in H6. 14, the nozzlebeing indicated at 1426 and the flame at 1402. In this case there is asharp line of demarcation between the carrier gas cone 1401 and theflame 1402, indicated at 1403.

With any of. the constructions in accordance with this invention,diffusion of the carrier gas into the flame takes place, so that thereis no sharp line of demarcation between the carrier gas cone and theflame, but on the com trary the carrier gas rapidly diffuses into theflame, carry ing the finely divided material with it. The flame producedwith the apparatus and method in accordance with this invention isrepresented schematically in FIG. 15, in which 1502 represents the flameand 1526 the nozzle. Carrier gas and entrained solid material particlesare distributed through the flame, as illustrated in FIG. 15 by lines inthe flame 1052.

In their previous constructions, material particles from the cone 1401from FIG. 14 received very little heat until they left the tip of thecone. However, afcr reaching the cone tip, such particles areaccelerated so rapidly by the flame that they have very little time inwhich to be heated thereafter. In the embodiment in accordance with thisinvention, such particles are introduced into the flame so that eachparticle is heated by the flame for a longer per od of time.

The function of the diffuser nozzle is not only to distribute theparticles throughout the flame by diffusion of the carrier gas into theflame, but to accomplish this result without using more carrier gas andpreferably by using less carrier gas. Additionally, the function of thediffuser nozzle is to accomplish these results and at the same time toreduce the velocity of the particles as they enter the flame.

When the carrier gas emerges from an open conduit, the velocity of thevarious elements of the stream of the carrier gas is not constant acrossthe stream cross-section. Due to skin friction, the velocity at theedges of the conduit will be materially less than the velocity in thecenter. This uneven carrier gas velocity has many disadvantages. Thevelocity in the center may be too great, causing the particles to passthrough the flame too rapidly, whereas the velocity at the edge of theflame, particularly at the bottom edge, may be too low to preventparticles from actually dropping out of the flame. It is this latterdropping out of the flame which frequently causes material to collecttemporarily on the nozzle tip and thereafter be blown as spatter on tothe work. The construction in accordance with this invention correctsthe diificulties that result from uneven carrier gas velocities byproviding a substantially even velocity across the cross-section of thecarrier gas stream a short distance beyond the nozzle tip.

Improvements in accordance with this invention result in high operatingefficiency of the process, so that not only may finer, less accuratelygraded materials be used, but there is in addition a materialimprovement in the deposit efficiency. Deposit efficiency is the ratioof weight of solid material fed into the gun to weight of materialdeposited on the base to be coated. Not only is the deposit efficiencyimproved by the construction in accordance with this invention, but therate of spraying, as measured by pounds of material per hour, isincreased with the same flame adjustments.

Example 1 Zirconia in finely divided powdered form is provided with aparticle size of from 2 to 50 microns. A gun in accordance with thepreferred embodiment, as described above, and with a nozzle illustratedin FIGS. 10 and ii, is attached to a source of acetylene, at a pressureof i5 p.s.i. gauge and a source of oxygen gas at 20 p.s.i. gauge.

The powdered material is placed in the gun hopper. The gun is lighted,as previously described, and the flame adjusted to be approximatelyneutral. The carrier gas valve is opened to approximately 6 clicks ofthe detent.

A 4" square by /4" thick mild steel plate, which is to be coated on onesurface, is first grit-blasted, using a 50%50% mixture of SAE G25 andSAE G40 steel grit, using a suction blast gun in the conventional mannerand a blasting air pressure of approximately 80 p.s.i.

The clean surface of the plate is pre-heated, using the gun to atemperature of approximately 250 F.

The powder feed trigger of the gun is then operated to produce powderflow and the gun used to spray the coating of the alloy. The gun nozzleis held about 6" from the surface of the plate.

It is desired in this case to have a finished thickness of .015".

The spraying speed was 2V2 pounds per hour of mate rial, and the depositefficiency, which is the ratio of the weight of the solid material fedinto the flame to the weight of the deposited coating, was 86%. A stronghard coating resulted.

With previous constructions operated exactly as described in the aboveexample, zirconia of a particle size from 10 to 40 microns would havebeen required and a deposit efficiency of only 46% would have beenobtained and a spraying speed of only 1 /2 pounds per hour would haveresulted. More skill would have been required by the operator to producethe hard coating produced in Example 1 without spatter.

The nozzle construction in accordance with this invention is highlysatisfactory for spraying tinciy divided metals as well as ceramicmaterials.

sition is provided in powdered form, with particle size such that allwill pass through a 120 mesh U.S. standard screen and not over 30% willpass through a 325 mesh US. standard screen:

A gun as described above and illustrated in the drawing is attached to asource of acetylene at a pressure of lbs. per square inch gauge and asource of oxygen gas at a pressure of lbs. per square inch gauge.

The powdered alloy is placed in the gun hopper. The gun is lighted, aspreviously described, and the flame adjusted to be approximatelyneutral. The carrier gas valve is opened to approximately 10 clicks ofthe detent.

A 4 square by /4-thick mild steel plate, which is to be coated on onesurface, is first grit-blasted, using a 50%50% mixture of SAE G and SAEG steel grit, using a suction blast gun in the conventional manner and ablasting air pressure of approximately p.s.i.

The clean surface of the plate is pro-heated, using the gun to atemperature of approximately 250 F.

The powder feed trigger of the gun is then operated to produce powderflow and the gun used to spray the coating of the alloy. The gun nozzleis held about 10" from the surface of the plate.

It is desired in this case to have a finished thickness after finalgrinding of .030". The coating is applied until it is between .045 and.050" thick.

The coating, which in this case will not get hotter than a few hundreddegrees, is allowed to cool in air to near room temperature.

The surface is then ground to the desired thickness, using a siliconcarbide wheel in the conventional manner.

The above examples are given to illustrate the invention and not tolimit the same.

The foregoing specific description is for purposes of illustration andnot of limitation and it is therefore our intention that the inventionbe limited only by the appended claims or their equivalents wherein wehave cn deavored to claim broadly all inherent novelty.

We claim:

1. in a spray gun for spraying finely divided, solid heatfusiblematerial, a discharge nozzle defining a central conduit and meansconnected thereto adapted to supply a stream of gas-borne, finelydivided, solid material thereto, a series of jets at least partiallysurrounding said central conduit, and means connected thereto adapted tosupply a stream of combustible gas mi ure thereto to pro udce a sheathof flame at least par t. lly surrounding the projection of said centralconduit, said central conduit terminating in a number of radiallydivergent passages to outwardly diffuse said stream of gas-borne solidmaterial into the space occupied by said sheath.

2. In a spray gun for spraying finely divided, solid heat-fusiblematerial, a discharge nozzle defining a central conduit and meansconnected thereto adapted to supply a stream of gas-borne, finelydivided, solid material thereto, a series of jets at least partiallysurrounding said central conduit, and means connected thereto adapted tosupply a stream of combustible gas mixture thereto to produce a sheathof flame at least partially surrounding the projection of said centralconduit, said central conduit terminating in a number of radiallydivergent passages to outwardly diffuse said stream of gas-borne solidmaterial into the space occupied by said sheath, and comprising, inaddition, air bleeder means extending from the side of said nozzle intothe space at the discharge end of said nozzle between said central ductand said sheath adapted to aspirate air into said space.

3. In a spray gun for spraying finely divided, solid heat-fusiblcmaterial, a discharge nozzle defining a central conduit and meansconnected thereto adapted to supply a stream of gas-borne. finelydivided. solid material thereto. 21 series of jets at least partiallysurrounding said central conduit, and means connected thereto adapted tosup ply 21 stream of combustible gas mixture thereto to produce a sheathof flame at least partially surroundIng the projection of said centralconduit, said central conduit terminating in a number of radiallydivergent passages to outwardly diffuse said stream of gas-borne solidmaterial into the space occupied by said sheath, and comprising, inaddition, an air hleeder including an annular groove UNITED STATESPATENTS Brierly May 19, 1953 Charlop et al Jan. 21, 1958 FOREIGN PATENTSGreat Britain May 18, 1942 Great Britain Jan. 16, 1952

1. IN A SPRAY GUN FOR SPRAYING FINELY DIVIDED, SOLID HEATFUSIBLEMATERIAL, A DISCHARGE NOZZLE DEFINING A CENTRAL CONDUIT AND MEANSCONNECTED THERETO ADAPTED TO SUPPLY A STREAM OF GAS-BORNE,FINELYDIVIDED, SOLID MATERIAL THERETO, A SERIES OF JETS AT LEASTPARTIALLY SURROUNDING SAID CENTRAL CONDUIT, AND MEANS CONNECTED THERETOADAPTED TO SUPPLY A STREAM OF COMBUSTIBLE GAS MIXTURE THERETO TO PRODUCEA SHEATH OF FLAME AT LEAST PARTIALLY SURROUNDING THE PROJECT ON OF SAIDCENTRAL CONDUIT, SAID CENTRAL CONDUIT TERMINATING IN A NUMBER OFRADIALLY DIVERGENT PASSAGES TO OUTWARDKT DUFFYSE SAID STREAM OFGAS-BORNE SOLID MATERIAL INTO THE SPACE OCCUPIED BY SAID SHEATH.